全文获取类型
收费全文 | 118篇 |
免费 | 1篇 |
国内免费 | 3篇 |
专业分类
测绘学 | 17篇 |
大气科学 | 32篇 |
地球物理 | 18篇 |
地质学 | 38篇 |
海洋学 | 11篇 |
综合类 | 3篇 |
自然地理 | 3篇 |
出版年
2023年 | 1篇 |
2022年 | 1篇 |
2021年 | 1篇 |
2020年 | 3篇 |
2019年 | 3篇 |
2018年 | 4篇 |
2017年 | 3篇 |
2016年 | 5篇 |
2015年 | 4篇 |
2014年 | 8篇 |
2013年 | 12篇 |
2012年 | 8篇 |
2011年 | 2篇 |
2010年 | 2篇 |
2009年 | 6篇 |
2008年 | 8篇 |
2007年 | 5篇 |
2006年 | 5篇 |
2005年 | 2篇 |
2004年 | 4篇 |
2003年 | 3篇 |
2002年 | 2篇 |
2001年 | 2篇 |
1999年 | 2篇 |
1998年 | 3篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1995年 | 2篇 |
1994年 | 1篇 |
1987年 | 1篇 |
1985年 | 1篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1977年 | 1篇 |
1974年 | 2篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1968年 | 1篇 |
1967年 | 2篇 |
1963年 | 1篇 |
1956年 | 1篇 |
排序方式: 共有122条查询结果,搜索用时 529 毫秒
121.
In this paper, a lattice-type model to simulate the micro-mechanical behaviour of particulate/granular media is presented. In this numerical model, a particulate assembly is simulated as a lattice/truss. Nodes located at contacts between a particle and its neighbours are linked by bars to each other. Each particle is represented by a lattice within its microstructure and particle interact through load transfer at the nodes. Constraints are prescribed at the nodes to describe active, deactivated and reactivated contacts. When a particulate assembly develops into a mechanism (deformation with zero incremental load), further deformation is simulated through a framework that describes the kinematics of the particles (sliding, rolling and rotation of particles). This framework is formed by introducing nodes at the particle centroids and linking them with bars. Bars-linking particles with a non-sliding contact are assigned large stiffnesses relative to bars linking particles with a sliding contact. Numerical tests are conducted on two-dimensional assemblies of disks, arranged as very loose and very dense packing under simple shear loading conditions. The results concord with the results of numerical tests conducted using the discrete element method and with photoelastic experiments. Additionally, the model is applied to study the effects of initial imperfections caused by particles with low elastic modulus. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献
122.
Nitrification, fuelled by ammonium is the pivotal oxidative pathway to nitrogen cycling. In spite of its ecological significance, the factors regulating nitrification rates in the benthic realm remain poorly understood. The present study therefore examines some of the factors like ammonium, nitrite, nitrate, organic carbon, iron and manganese on down-core variability in benthic nitrification rates in two different mangrove ecosystems, one under the influence of ferromanganese ore mining (experiment) and the other relatively undisturbed (control). We hypothesize that besides organic carbon, iron could also influence the rate of nitrification. The study also contrasts the distributive pattern of autotrophic and heterotrophic nitrifiers in the two regions. The concentration of iron at the control site ranged from 1.1% to 15.1% while at the experimental site it ranged from 2.9% to 46%. The levels of organic carbon at control and experimental sites ranged from 0.02% to 6.9% and 0.1% to 6.5%, respectively. The nitrification rates at the control and experimental sites are comparable and ranged from 3.2 ± 1.2 to 18.4 ± 1.9 ng at-N g(sediment)−1 h−1 and 2.7 ± 1.5 to 18.2 ± 0.6 ng at-N g(sediment)−1 h−1, respectively. While the abundance of heterotrophic nitrifiers at both the sites ranged from 102–3 cells g−1 sediment, the autotrophic nitrifiers at the experimental site was higher by an order at 103 cells g−1 sediment reflecting the relatively higher refractile nature of organic carbon at the experimental site (Straus and Lamberti, 2000). Though organic carbon and nitrification rates are similar in both the sites, the underlying mechanisms governing the processes could be different. Our studies suggest that at the control site, heterotrophic nitrifiers govern nitrification rates (r = 0.28, p < 0.05, n = 64) using organic carbon (r = 0.32, p < 0.01, n = 64). At the experimental site, nitrification was governed more by autotrophic nitrifiers (r = 0.43, p < 0.001, n = 64) at the expense of iron (r = 0.47, p < 0.001, n = 64). Therefore at the experimental site with higher load of iron, autotrophic nitrification could be more important. It is therefore inferred that both the quality of organic carbon and quantity of iron govern nitrification rates in these mangrove swamps. 相似文献